This invention relates to lighting systems in automobiles. More specifically, this invention relates to a barrier coating on top of the metallized reflector in a headlight assembly in automobiles.
Conventionally, motor vehicles have either one or two pairs of headlights that perform the function of illuminating drivers filed of vision. In order to reflect the light, the headlights are provided with a headlamp reflector. The headlamp reflector is coated with a reflective metallic coating. However, in order to protect the reflective coating of the reflector, protective coatings have been coated on top of such reflective coating. Typically, the protective coating is hexa-methyl di-siloxane (HMDSO) applied directly on top of the reflective coating by plasma polymerization in the same chamber used for metallization of the reflective coating. Although the process used to apply the protective coating is suitable for applying the coating at high rate, it has a number of disadvantages.
One of the major disadvantages of the HMDSO protective coating is that the low surface energy of the HMDSO can tend to cause a fogging appearance of the reflective layer due to air humidity and/or vapors from the headlights components. Another disadvantage of the HMDSO protective coating is that oxygen from the coating can oxidize the reflective metallization. In particular, experiments have shown that the oxygen attacks the copper in copper/aluminum gold colored reflective coatings, turning the color dark and also resulting in loss of reflectivity.
Other prior art have devised a method of coating the reflective layer with HMDSO and further coating the HMDSO layer with a hydrophilic layer. However, this method of first coating the reflective surface with HMDSO and then with a hydrophilic layer increases the processing time and also the cost of production, and does not prevent oxidation of the metallic reflective coating.
Therefore, there is a need in the industry to provide a better barrier coating on the reflective surface to prevent the fogging and the oxidation process described above. Also, there is a need in the industry to apply such barrier coating in a single process.
In accordance with the preferred embodiment of the present invention, a headlight assembly installed in a motor vehicle has a transparent barrier coating deposited directly on top of the reflective metallic coating. Preferably, the headlight assembly is provided with a reflector and a light source. The interior surface of the reflector is first coated with a reflective layer. A second layer of a barrier coating is deposited on top of the reflective coating by the process of plasma polymerization. The material used as the barrier coating is an organic carbon compound that is free of any electronegative group such as oxygen.
In another aspect of the invention a method of coating an interior surface of a headlight assembly installed in a motor vehicle is disclosed. The method comprises the steps of depositing a first layer of a highly reflective material and depositing a second layer on top of the first layer of an organic carbon compound by the plasma polymerization process.
Further aspects, features and advantages of the present invention will become apparent from consideration of the following description and appended claims when taken in connection with the accompanying drawings.